The transcritical transition of the nonpolar hydrocarbon and highly polar alcohol mixtures from the subcritical to supercritical regime has not been yet well understood. In the present paper, based on molecular dynamics simulation, the nonequilibrium evaporation and transcritical transition processes of the n-heptane/ethanol mixtures are comprehensively investigated under various ambient conditions, and the development of the vapor-liquid interface is deeply analyzed. Under the sub-critical condition, the increased ethanol concentration elevates the evaporation rate because of the decreased vapor pressure and increased thermal conductivity. However, under the supercritical condition, the effect of ethanol addition on the mixture temperature becomes slight due to the decreased difference of thermal conductivity between ethanol and n-heptane, but the preferential diffusion of ethanol is observed because of its higher diffusivity. In addition, it is found that the increase of ethanol broadens the vapor-liquid interface at moderately high pressure due to its higher volatility and thermal conductivity. Since the interfacial thickness affects the interfacial resistivities and evaporation characteristics in the hydrodynamic framework, the thickened interface indicates the more significant nonequilibrium effect in the vicinity of interface for the mixtures with large amounts of ethanol. Finally, the transcritical transition time decreases rapidly with the increased ambient pressure, and the descent gradient gradually decreases with the further increased pressure because the thermal conductivity becomes less sensitive to the pressure.

中文翻译：

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通过分子动力学模拟分析正庚烷/乙醇混合物的亚临界到超临界转变

非极性烃和高极性醇混合物从亚临界状态到超临界状态的跨临界转变尚未得到很好的理解。在本文中，基于分子动力学模拟，n的非平衡蒸发和跨临界跃迁过程对各种环境条件下的-庚烷/乙醇混合物进行了全面研究，并对气液界面的发展进行了深入分析。在亚临界条件下，由于蒸汽压降低和热导率增加，乙醇浓度的增加提高了蒸发速率。然而，在超临界条件下，由于乙醇和n之间的热导率差异减小，乙醇添加对混合物温度的影响变得很小-庚烷，但观察到乙醇的优先扩散，因为它具有较高的扩散率。此外，发现乙醇的增加由于其较高的挥发性和热导率而在中等高压下拓宽了汽液界面。由于界面厚度影响流体动力学框架中的界面电阻率和蒸发特性，加厚的界面表明与大量乙醇的混合物在界面附近的非平衡效应更为显着。最后，跨临界转变时间随着环境压力的增加而迅速减少，并且下降梯度随着压力的进一步增加而逐渐减小，因为热导率对压力变得不那么敏感。